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arXiv 2104.14903nucl-exhep-phnucl-th
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LHC上PbPb碰撞中电弱玻色子产生的中心性依赖

Centrality dependence of electroweak boson production in PbPb collisions at the LHC

Florian Jonas, Constantin Loizides

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8 pages, 5 figures, 1 table, comments welcome
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摘要：

在$\sqrt{s_{\rm nn}}=5.02$ TeV的PbPb碰撞中，由ATLAS合作测量的W和Z玻色子产生的核修改的最新数据显示了外围碰撞的增强，似乎与Glauber模型的预测相矛盾。以前的数据解释，认为核子-核子截面可能是阴影在核-核碰撞，因此抑制相比，质子-质子截面在相同的碰撞能量。这种解释对于理解重离子数据，特别是在Glauber模型的背景下，具有相当重要的意义。相反，我们通过假设测量的中心性确定存在轻微偏倚，对相关系统不确定性的大小提供了另一种数据解释。利用这一假设，我们表明，数据与理论计算使用核部分子分布函数。最后，我们推测，W $^-$ /W $^{+}$比率的中心性依赖性可能指向Pb核的较大皮肤厚度的相关性，如果存在的话，将导致比目前在Glauber模型中占比大几个百分点的PbPb截面，因此可能是中心性偏差的根源。

英文摘要：

Recent data on the nuclear modification of W and Z boson production measured by the ATLAS collaboration in PbPb collisions at $\sqrt{s_{\rm nn}}=5.02$ TeV show an enhancement in peripheral collisions, seemingly contradicting predictions of the Glauber model. The data were previously explained by arguing that the nucleon-nucleon cross section may be shadowed in nucleus-nucleus collisions, and hence suppressed compared to the proton-proton cross section at the same collision energy. This interpretation has quite significant consequences for the understanding of heavy-ion data, in particular in the context of the Glauber model. Instead, we provide an alternative explanation of the data by assuming that there is a mild bias present in the centrality determination of the measurement; on the size of the related systematic uncertainty. Using this assumption, we show that the data is in agreement with theoretical calculations using nuclear parton distribution functions. Finally, we speculate that the centrality dependence of the W$^-$/W$^{+}$ ratio may point to the relevance of a larger skin thickness of the Pb nucleus, which, if present, would result in a few percent larger PbPb cross section than currently accounted for in the Glauber model and may hence be the root of the centrality bias.

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